The present invention relates to a connection for a tubular member and more particularly to an end connection for a capillary tube. The invention moreover relates to a quick-connect for a chromatographic capillary tube column.
In one class of chromatographic methods, electrically neutral analytes are entrained by a mobile fluid which carries them down the bore of a capillary tube or column. Analytes undergo partitioning between this mobile fluid, or mobile phase, and a stationary phase coating the inner wall of and/or packing interior to, the capillary bore. In this class of chromatography, the mobile phase may be gas, liquid or supercritical fluid giving rise to methods and apparatus commonly known as capillary gas chromatography, microbore liquid chromatography or supercritical fluid chromatography, respectively.
In another class of chromatographic methods, electrically charged analytes are propelled by an electric field through a stationary phase filling the bore of a capillary tube. This class of methods and apparatus is commonly known as capillary zone electrophoresis.
In prior art forms of capillary chromatography, capillary columns are sealed into sample injector means and sample detection means using tapered deformable seals or ferrules through which the columns are inserted. The ferrules are deformed under pressure supplied by an external torqued hexagonal nut, which forces the ferrule taper against a tapered metallic seat such that the ferrule contracts radially about the capillary column inserted through the ferrule, thus effecting a tight seal. Ferrules of this type are preferably high-temperature plastic deformable ferrules. Graphite-Vespel.RTM. ferrules are preferred.
In chromatography, it is important to be able to quickly connect the ends of a chromatographic column to both an injection device for feeding a sample and a detection device for analyzing the sample after it has travelled through the length of the column. It is also important to be able to quickly change capillary tubes.
One process of changing a capillary gas chromatographic column has been widely employed. A nut and ferrule are slipped over the end of a capillary tube. Following insertion through the ferrule, the operator cleaves a small length of capillary tube from the end of the column to be sure the operative column end is open and free of small particles or ferrule shavings which would obstruct the flow of mobile phase during chromatographic separation. The operator then gathers the nut and ferrule together along the length of the column, and draws the end of the column into proximity to the forward end of the ferrule. Immobilizing the column position relative to the ferrule end with one hand, the operator paints a mark on the column near the back of the nut using, for example, Liquid Paper.RTM., commonly used to cover typographical errors in typed documents. The operator then memorizes the position of the spot relative to the back of the nut. The nut/ferrule/column combination is then inserted into, for example, an injector port of a capillary gas chromatograph. The nut is tightened partially, and the column pulled to align the painted spot to its original position relative to the rear of the hexagonal nut. This positions the end of the capillary tube relative to the ferrule tip, a positioning critical to proper function of the injection means. The nut is then tightened. This procedure is repeated for the other end of the column, which is sealed into a detector port.
Methods of this type for sealing capillary columns into gas chromatographs suffer numerous disadvantages. Considerable manual dexterity is required of the operator to position the end of the column in proper spatial relation to the ferrule tip. Because columns are mounted in oven structures that are generally small and positioned below shoulder height on laboratory benches, operators must perform dexterous operations in cramped regions while bending over, in the case of top loading ovens, or squatting down and straining upwards in the case of front loading ovens. It is not uncommon for the nut and ferrule assembly to slip at some point in the installation process, often becoming entangled or mechanically engaged with wire frame cages on which columns are mounted, with resulting inconvenience and occasional column damage. Threaded fittings and nuts wear out and have to be replaced, further adding to the cost and inconvenience of known gas chromatographs. Column positioning errors commonly cause dead volume in injectors or detectors, which leads to undesirable tailing of chromatographic peaks. In capillary column manufacturing operations, particularly quality testing, in which large numbers of columns must be connected and disconnected on a daily basis, operator fatigue can reduce overall production efficiency and increase production costs. Wrenches used to tighten ferrule nuts are often dropped, resulting in damage to expensive capillary columns. Also, operators often accidentally paint fingers and gloves with the marking fluid.
The aforementioned disadvantages, which present problems in capillary gas chromatography, also present problems in other forms of capillary chromatography.